基带FH-OFDM频率映射与碰撞分析
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摘要
宽带无线接入和宽带移动通信的基本传输和多址技术都是基于OFDM技术的。在LTE中,上行链路采用单载波频分多址(SC-FDMA),实现方式为离散傅里叶变换扩展OFDM (DFT-S-OFDM)技术,下行链路采用正交频分多址(OFDMA)技术。OFDM由于采用多路并行传输,因此可以提高信息的传输速率,子载波相互正交,使之可以部分重叠,从而提高了频谱利用率。由于不同的频率,其衰落极点不一样,而跳频技术可以避免通话长时间位于衰落极点处,从而达到干扰分集的作用。
将跳频和OFDM技术结合起来,不仅能发挥两者共同的优势,通过选择适当的结合方式,还能降低跳频实现的复杂度。随着通信技术的发展,在LTE上行共享信道(PUSCH)中已经有了跳频方案,IEEE802.20也采用了基于调度或者跳频的OFDMA,跳频OFDM将逐渐受到重视。
本文首先学习和分析研究多载波跳频OFDM和传统的射频跳频OFDM以及基带跳频OFDM实现过程。由于射频跳频OFDM系统中,OFDM调制和跳频调制可看成是两个独立的模块,虽然结合了两者的优点,但实现复杂度依然没有降低,本文将跳频的实现放在OFDM调制部分实现,让子载波进行跳变,不用产生新的频率,相当于是对信息进行一次预编码,实现起来要容易的多。
其次,由于基带跳频OFDM的关键在于子载波跳频映射,因此本文重点研究跳频映射方法和由此带来的频率碰撞问题。在研究了循环跳频的机理之后,给出两种实现方法,一种是DFT矩阵变换实现跳频,另一种是补零法实现跳频,并进行了matlab仿真和分析。由于循环跳频和DFT矩阵变换实现跳频,在OFDMA-FH分布式实现过程中不易实现,本文在补零法基础上,引用了分组跳频和独立随机跳频方式进行子载波跳频映射。在进行频率碰撞的理论分析之后,还通过matlab进行了仿真分析与比较,仿真结果表明两种跳频方式产生的碰撞符号数和理论值吻合,并且两种跳频方式所产生的误符号数相等。
The basic transmission and multiple access techniques of broadband wireless access and broadband mobile communications are both based on OFDM technology. The uplink used single carrier frequency division multiple access (SC-FDMA) which is realized by the extended discrete Fourier transform OFDM (DFT-S-OFDM) technology, and the downlink uses orthogonal frequency division multiple access (OFDMA) technology in LTE. As OFDM uses multiple parallel transmission technology, it can improve the information transfer rate, moreover, the sub-carriers are orthogonal to each other, so that it can partially overlap, which can improve spectral efficiency. Because of different frequencies, the fading of poles are not the same, and the frequency hopping technology can avoid frequency hit at the fading poles for a long time which can achieve frequency diversity.
The combination of frequency hopping and OFDM technology can not only play advantages of the both, but also reduce the frequency hopping implementation complexity by selecting the appropriate combination. As the development of communication technology, the uplink shared channel (PUSCH) in LTE has been used frequency hopping scheme, the IEEE802.20also uses OFDMA based on scheduling or frequency hopping, frequency hopping OFDM will be gradually taken seriously.
Firstly, the implementation process of multi-carrier frequency-hopping OFDM and RF frequency hopping OFDM include baseband frequency hopping OFDM are studied and analyzed in this thesis. In the RF frequency hopping OFDM system, OFDM modulation and frequency hopping modulation can be regarded as two separate modules, although combines the advantages of both, the implementation complexity is not reducing. And the realization of the frequency hopping OFDM in baseband is equivalent to precode with information, let the subcarriers to jump, need not produce new frequency, it's easy to achieve.
Secondly, the key lies in the baseband frequency hopping OFDM is sub-carrier frequency hopping mapping, so the thesis focused on frequency-hopping mapping method and the frequency collision problems. In the study of cycle frequency hopping mechanism, two ways of realizing frequency hopping are given, one is DFT matrix transform, the other is zero-padding method, and Matlab simulation and analysis are done. As cycle frequency hopping and DFT matrix transformation frequency hopping is not easy to achieve in a distributed implementation of FH-OFDMA, the thesis refers to the packet frequency hopping and independent random hopping sub-carrier mapping, conducting a theoretical analysis of the collisions of frequency and simulating by Matlab, the simulation results shown that the collision probability of the two hopping style are equal to the theoretical result, and the number of error symbols generated by the two hopping are equal.
将跳频和OFDM技术结合起来,不仅能发挥两者共同的优势,通过选择适当的结合方式,还能降低跳频实现的复杂度。随着通信技术的发展,在LTE上行共享信道(PUSCH)中已经有了跳频方案,IEEE802.20也采用了基于调度或者跳频的OFDMA,跳频OFDM将逐渐受到重视。
本文首先学习和分析研究多载波跳频OFDM和传统的射频跳频OFDM以及基带跳频OFDM实现过程。由于射频跳频OFDM系统中,OFDM调制和跳频调制可看成是两个独立的模块,虽然结合了两者的优点,但实现复杂度依然没有降低,本文将跳频的实现放在OFDM调制部分实现,让子载波进行跳变,不用产生新的频率,相当于是对信息进行一次预编码,实现起来要容易的多。
其次,由于基带跳频OFDM的关键在于子载波跳频映射,因此本文重点研究跳频映射方法和由此带来的频率碰撞问题。在研究了循环跳频的机理之后,给出两种实现方法,一种是DFT矩阵变换实现跳频,另一种是补零法实现跳频,并进行了matlab仿真和分析。由于循环跳频和DFT矩阵变换实现跳频,在OFDMA-FH分布式实现过程中不易实现,本文在补零法基础上,引用了分组跳频和独立随机跳频方式进行子载波跳频映射。在进行频率碰撞的理论分析之后,还通过matlab进行了仿真分析与比较,仿真结果表明两种跳频方式产生的碰撞符号数和理论值吻合,并且两种跳频方式所产生的误符号数相等。
The basic transmission and multiple access techniques of broadband wireless access and broadband mobile communications are both based on OFDM technology. The uplink used single carrier frequency division multiple access (SC-FDMA) which is realized by the extended discrete Fourier transform OFDM (DFT-S-OFDM) technology, and the downlink uses orthogonal frequency division multiple access (OFDMA) technology in LTE. As OFDM uses multiple parallel transmission technology, it can improve the information transfer rate, moreover, the sub-carriers are orthogonal to each other, so that it can partially overlap, which can improve spectral efficiency. Because of different frequencies, the fading of poles are not the same, and the frequency hopping technology can avoid frequency hit at the fading poles for a long time which can achieve frequency diversity.
The combination of frequency hopping and OFDM technology can not only play advantages of the both, but also reduce the frequency hopping implementation complexity by selecting the appropriate combination. As the development of communication technology, the uplink shared channel (PUSCH) in LTE has been used frequency hopping scheme, the IEEE802.20also uses OFDMA based on scheduling or frequency hopping, frequency hopping OFDM will be gradually taken seriously.
Firstly, the implementation process of multi-carrier frequency-hopping OFDM and RF frequency hopping OFDM include baseband frequency hopping OFDM are studied and analyzed in this thesis. In the RF frequency hopping OFDM system, OFDM modulation and frequency hopping modulation can be regarded as two separate modules, although combines the advantages of both, the implementation complexity is not reducing. And the realization of the frequency hopping OFDM in baseband is equivalent to precode with information, let the subcarriers to jump, need not produce new frequency, it's easy to achieve.
Secondly, the key lies in the baseband frequency hopping OFDM is sub-carrier frequency hopping mapping, so the thesis focused on frequency-hopping mapping method and the frequency collision problems. In the study of cycle frequency hopping mechanism, two ways of realizing frequency hopping are given, one is DFT matrix transform, the other is zero-padding method, and Matlab simulation and analysis are done. As cycle frequency hopping and DFT matrix transformation frequency hopping is not easy to achieve in a distributed implementation of FH-OFDMA, the thesis refers to the packet frequency hopping and independent random hopping sub-carrier mapping, conducting a theoretical analysis of the collisions of frequency and simulating by Matlab, the simulation results shown that the collision probability of the two hopping style are equal to the theoretical result, and the number of error symbols generated by the two hopping are equal.
引文
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[40]艾渤,王劲涛,钟章队.宽带无线通信OFDM系统同步技术[M],人民邮电出版社,2011.
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[2]Van Nee, R.D.J.,and Prasad, R.:OFDM for wireless multimedia communications[M](Artech House, Boston, MA, 2000).
[3]Hara, S., and Prasad, R.:Multicarrier techniques for 4G mobile communications[M](ArtechHouse, Boston, MA, 2003).
[4]Saltzberg, R.:Performance of an efficient parallel data transmission system[J], IEEE Trans. Commun., 1967,15, pp. 805-811.
[5]Bingham, J.A.C.:Multicarrier modulation for data transmission:an idea whose time has come[J],IEEE Commun. Mag.,1990,28, (5), pp.5-14.
[6]Jung, P., Berens, F., and Plechinger, J.:A generalized view on multicarrier CDMA mobile radio systems with joint detection[J],Frequenz,1997, Part I: 51, (7-8); Part II: 51(11-12).
[7]Kaiser, S.:OFDM-CDMA versus DS-CDMA:performance evaluation for fading channels[C].Proc. IEEE Int. Conf. on Communications (ICC'95), Seattle, WA, USA, 1995, pp.1722-1726.
[8]Galda, D., and Rohling, H.:A low complexity transmitter structure for OFDM-FDMA uplink systems[C]. Proc. 55th IEEE Vehicular Technology Conf. (VTC 2002-Spring), 2002, pp.1737-1741.
[9]T Scholand, T Faber, A Seebens, J Lee, J Cho, Y Cho, H W Lee, P Jung. Fast frequency hopping OFDM concept[J]. Electronics Letters, 2005,41(13).
[10]梅文华,跳频通信[M].北京：国防工业出版社.2005.
[11]G. Parsaee, and A. Yarali, OFDMA for the 4th Generation Cellula networks[C](CCECE 2004), Niagara falls, Canada.May 2-5,2004.
[12]Chang R W. Synthesis of band-limited orthogonal signals for multichannel data transmission [J]. Bell Sythems Technical Journal,1966,45(10):1775-1796
[13]Radio Spectrum Management Group.A draft band pan for digital audio broadcasting [S]ECD 2000/5.December 2000
[14]ETS 300 401.Digital audio broadcasting (DAB);DAB to mobile,portable and fixed receivers [S].
[15]ETS 300 744.Digital broadcasting systems for television,sound and data services;framing structure,channel coding and modulation for digital terrestrial television[S]. May 1996
[16]IEEE P802.11a/D7.0. draft supplement tu standard for information technology telecommunications and information exchange between systems-local and metropolitan area networks-specific requirements —part II wireless LAN medium access control(MAC) and physical layer (PHY) specifications:high speed physical layer in the 5GHz band[S].July 1999
[17]Network and Customer Installation Interfaces—Asymmetric Digital Subscriber Line (ADSL) Metallic Interface[S], ANSI standard T1.413,1995
[18]3GPP TR36.913 V8.0.0. Requirements for further advancements for E-UTRA (LTE-Advanced) [S].June 2008.
[19]K.C.Chang. J.W.lin, and T.D.Chiueh, Design of A Downlink Baseband Receiver for IEEE 802.16e OFDMA Mode in High Mobility[C],in proc.of IEEE international SOC Conference,Oct 2007,pp.301-304.
[20]C.C Chang, C.H.Su, and J.M.Wu, A Low Power Baseband OFDM Receiver IC for Fixed WiMAX Communication[C], in proc. Of IEEE Aisa Solid-State Circuits Conf, Nov 2007.
[21]沈嘉,索士强,全海洋.3GPP长期演进(LTE)技术原理与系统设计[M].北京：人民邮电出版社,2009.
[22]胡宏林,徐惊.3GPP LTE无线链路关键技术[M]。北京：电子工业出版社,2008.
[23]中国军事百科全书边审委员会[M]。中国军事百科全书：军事技术。北京：军事科学出版社,1997
[24]朱刚,谈振辉,周贤伟.蓝牙技术原理与协议[M]。北京：北方交通大学出版社,2002
[25]E. Lance and G. K. Kaleh, A diversity scheme for a phase-coherent frequency-hopping spread-spectrum system[J], IEEE Trans. Commun., vol.45, no.9, pp.1123-1129, Sept. 1997.
[26]M. Ebrahimi and M. Nasiri-Kenari,Performance analysis of multicarrier frequency-hopping (MC-FH) code division multiple-access system:uncoded and coded schemes[J], IEEE Trans. Vehicular Technology, vol.53, no.4, pp.968-981, July 2004.
[27]O. S. Shin and K. B. Lee, Performance comparison of FFH and MCFH spread-spectrum systems with optimum diversity combining infrequency-selective Rayleigh fading channels[J], IEEE Trans. Commun.,vol.49, pp. 409-416, Mar. 2001
[28]单娜娜,侯春萍,基于IEEE802.20办议FLASH-OFDM系统的仿真与研究[J],天 津大学,《硅谷》2008年21期
[29]M. iang, L. Hanzo. Multiuser MIMO-OFDM systems using subcarrier Hopping[J]. IEE Proceedings:Communications.2006, 153(6):802-809
[30]B.C. Jung, D.K. Sung. Random FH-OFDMA System Based on Statistical Multiplexing[C]. IEEE 61st Vehicular Technology Conference. 2005,3:1793-1797.
[31]A. Al-Dweik, F.Xiong.Frequency-Hopped Multiple-Access Communications With Noncoherent M-ary OFDM-ASK[J]. IEEE Transactions on Communications. January 2003.
[32]Lisheng Fan; Jing Li; Yuanmo Lin; Xianfu Lei; Feifei Gao; Yongquan Jiang;, A novel group frequency-hopping scheme for OFDM modulated multiuser system[J], Systems and Control in Aeronautics and Astronautics (ISSCAA),2010 3rd International Symposium on, vol., no., pp.1178-1181,8-10 June 2010
[33]曾菊玲,金力军OFDM跳频通信系统设计[J].移动通信.2004.
[34]张伟明,刘宁庆.子载波跳频OFDM系统抗干扰性能研究[D].2008
[35]Tobias Scholand, Thomas Faber, Juho Lee, Joonyoung Cho, Yunok Cho and Peter Jung. Physical Layer Performance of a Novel Fast Frequency Hopping-OFDM Concept"[OL]. http://www.eurasip.org/content/Eusipco/IST0.5/papers/263.pdf
[36]T. Kurt and H. Deli?, On symbol collisions in FH-OFDMA[C], in Proc. 59th Semiannual IEEE Vehicular Technology Conf., Milano,Italy, May 2004, pp. 1859-1863.
[37]Stamatiou, K., Proakis, J.:A performance analysis of coded frequency-Hopped OFDMA[C]. In:Proc. IEEE Wireless Commun. Networking Conf., pp.1132-1137,2005
[38]田玉良,姚英,差分跳频技术分析[J],现代电子技术,2006年第19期
[39]佟学俭,罗涛OFDM移动通信技术原理与利用[M],人民邮电出版社,2003.
[40]艾渤,王劲涛,钟章队.宽带无线通信OFDM系统同步技术[M],人民邮电出版社,2011.
[41]A. Batra, J. Balakrishnan, G Aiello, J. Foerster and A. Dabak, Designof a multiband OFDM system for realistic UWB channel environments [J],IEEE Transactionson Microwave Theory and Techniques, pp.2123-2137, Sept.2004.
[42]B. Daneshrad, L. Cimini, M. Carloni, and N. Sollenberger,Performanceand implementation of clustered-OFDM for wireless communications [J],Mobile Netw. Appl., vol.2, no.4, pp.305-314,1997.
[43]L.Cimini and N. Sollenberger, Receiver srmcrure for multiple access OFDM[C], Record of the 49th IEEE Vehicular Technology Conference.Vol.1, Houston, USA, pp.468-472. May 1999.
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